METHOD FOR DECORATIVELY COATING A SUBSTRATE

Abstract: A substrate is provided with a decorative coating of grained appearance by applying to an opaque surface of the substrate a substantially continuous layer comprising a particulate material and an aqueous polymer binder, and discontinuously removing part of the layer (preferably in streaks or veins) so as to selectively expose part of the opaque surface, the particulate material and the partially removed layer both being lighter in colour than the opaque surface.

Description: METHOD FOR DECORATIVELY COATING A SUBSTRATE The present invention is concerned with a decorative method, and particularly a decorative method for providing a grained appearance on a substrate, such as a method of simulating the appearance of limed wood (especially oak) or the like. Grain imitation techniques are known in which a scumble glaze is applied to a painted wood substrate, the scumble glaze being applied in a streaky discontinuous manner to give the appearance of natural graining. Currently used techniques however are very time consuming and require considerable expertise, such as that of a craftsman, to create a desired natural grain appearance. They do not therefore appeal to amateur (that is, "do-it-yourself") painters, who represent an increasingly important part of the market. I have now developed a method which helps alleviate the above problems and which has been found to have its own aesthetic attraction to home owners. According to the present invention there is provided a method of providing a decorative coating for an opaque surface, which method comprises applying to said opaque surface a substantially continuous layer comprising an intimate mixture comprising a particulate (preferably non film-forming) material and an aqueous film-forming polymer binder, said particulate material and said layer both being lighter in colour than said opaque surface, and discontinuously removing part of said layer (preferably in streaks) so as to selectively expose part of said opaque surface. Any experienced professional or amateur painter will know instinctively the difference between lighter and darker shades of colour, as a result of judgement by eye. However, if needed, guidance can be gained from the international system of colour definition known as the "NCS". The NCS is described in the "ICI Colour Dimensions Colour Atlas" published by Imperial Chemical Industries Pic of London in 1986 ("Colour Dimensions" is a registered trade mark of Imperial Chemical Industries). The NCS defines colour in terms of a cypher, the first two digits of which extend from 00 to 99 with 00 representing white (that is, the ultimate lightness) and 99 representing black with the intermediate values from 01 to 98 representing increasingly darker shades. Lighter shades therefore have a lower pair of first digits. It is preferred that the particulate material and the continuous layer have an NCS value at least 10 units lower than that of the surface. The particulate material is typically an inorganic material, which may be hydrated, such as plaster (gypsum), clay or the like, or non-hydrated, such as chalk or titanium dioxide. When an inorganic material is used, it is advantageous that the intimate mixture used in the method according to the invention may be fire retardant. Alternatively, an organic particulate material, such as hollow or alveolate beads of polystyrene or the like, or finely chopped fibres may be used. Suitable organic beads are described for example in European patent specification 0113435B (the contents of which are herein incorporated by reference). The particulate material is intimately mixed with the aqueous polymer binder, preferably together with thixotropising material, such as a polyurea adduct or bentonite clay, so as to provide a thixotropic mixture. It may be preferred that the intimate mixture further comprises reinforcing fibres which can serve to strengthen a resulting coating provided on the opaque surface. Advantageously the intimate mixture further comprises a drying retardant (a material which retards drying of the coating). The use of a drying retardant is beneficial in allowing the mixture to be applied as a substantially continuous layer and further allowing subsequent removal thereof before substantial drying of the layer has occurred. A preferred drying retardant comprises a gel material. Examples of gels suitable for use as a drying retardant are cellulose-based products such as carboxymethyl cellulose, hydroxymethyl cellulose and methyl cellulose, acrylamide and acrylate polymers and copolymers, gelatin, polysaccharides, polyoxamers (polyoxyethylene-polyoxypropylene block copolymers), pectins and agar. It is preferred that the aqueous polymer binder is translucent. Preferably the binder comprises an aqueous dispersion of particles of polymer which are capable of coalescing as the dispersion dries so as to form a film of polymeric material. Suitable polymers include polymers and copolymers of esters such as methyl, ethyl, propyl and hexyl esters of acrylic or methacrylic acids optionally with acrylic or methacrylic acid or polymers or copolymers of vinyl esters including vinyl acetate. Certain copolymers of these types are now available as aqueous solutions as opposed to dispersions. The aqueous polymer binder may, in some cases, contain a minor proportion by weight of an organic solvent, which should be miscible with water. An example of such a solvent is an alcohol. It is preferred that the intimate mixture comprises substantially equal amounts of an aqueous carrier, typically water, and the particulate material, the aqueous carrier and particulate material being present in excess of the polymer binder. A preferred intimate mixture comprises 4 to 6 parts by weight of the particulate material, 4 to 6 parts by weight of water optionally 0 to 2 parts organic (preferably alcoholic) co-solvent to assist film formation and 0.5 to 3 parts by weight of the aqueous polymer binder. In a particularly preferred embodiment of the present invention, wherein the intimate mixture further comprises a drying retardant substantially as hereinbefore described, the preferred intimate mixture includes 0.5 to 3 parts by weight of the drying retardant. The opaque surface may be provided by wood, plastics, metal or the like, and it should have a darker colour than the intimate mixture. In some embodiments it is preferred that the substrate comprises wood. The invention is particularly advantageous in enabling the production of an article having a grained appearance, such as that simulating limed oak, a pine effect, or the like. The substrate may, for example, be timber, or a fibre board such as MDF (medium density fibre board). Advantageously the substrate comprises a building structure such as a wall panel, door, window frame or the like. Alternatively the substrate may comprise a furniture component such as a fitted kitchen or bedroom unit, cupboard door, table, seat or the like. In some embodiments, the substrate comprises at least one generally planar surface which is required to have a grained appearance as described above. It is preferred that the method involves applying an opaque protective or decorative coating to the substrate so as to provide the latter with a sufficiently dark opaque surface substantially as hereinbefore described. The opaque coating is preferably applied so as to substantially cover an exposed surface of the substrate. Preferably the opaque coating is water based, although organic solvent-based coatings may be employed. It is further preferred that the method involves applying a translucent or transparent coating (such as a varnish, which is preferably water-based), over the discontinuous decorative coating described above. The translucent or transparent coating may itself contain a stain material, pigment, dye or the like; alternatively a stain may be applied to the translucent or transparent coating. The opaque surface typically comprises a paint selected to provide a surface of the substrate with a desired base colour. A particularly preferred colour of the opaque surface is brown or beige, which can contrast with the lighter colour of the intimate mixture, and give the appearance of a naturally grained effect. Further preferred colours of the opaque surface include grey, or other background colours, such as blue, green, red, yellow or the like. The particulate material preferably has a white, cream, beige or brown colour which contrasts with the darker colour of the opaque surface. Examples of such colours are Y 00 R (usually written as "Y") up to Y 90 R according to the NCS definition referred to above. The particulate material may advantageously be mixed with colorants or the like to provide the intimate mixture with a desired colour. The colour combination of the opaque surface and the intimate mixture is advantageously selected to simulate a grained appearance of a desired wood effect. The decorative coating may be applied by brushing, pad spreading, rolling or spraying onto the opaque surface. Advantageously the decorative coating is allowed to substantially dry (typically for at least one hour) before subsequent application of the intimate mixture thereon. The intimate mixture is preferably similarly applied to the opaque surface by brushing, pad spreading, rolling or spraying thereon. The intimate mixture is preferably applied to provide a substantially continuous layer having a thickness (prior to drying) in the range of 0.3 to 2mm. The thickness of the layer is selected to provide an appearance of a desired grain, a preferred thickness being about 0.5mm. It is preferred that removal of the continuous layer involves at least two stages. In the first stage, it is preferred that the continuous layer is discontinuously removed in non¬ linear streaks to give the opaque surface a veined, streaked or grained appearance, preferably using a comb member including a plurality of distal teeth, the comb member being drawn along the opaque surface to provide a veined appearance resembling that of natural grain. Preferably the tips of the teeth each respectively comprise a contact edge extending for about 2 to 5mm in the general direction of the comb member, the tips advantageously being spaced apart by about 2 to 10mm. Advantageously, in a second stage of the removal of the continuous layer, it is preferred that the veined, grained or streaked surface is treated with at least one tool member having a plurality of spaced apart proud formations (typically of plastics or elastomeric material or the like), to selectively expose parts of the opaque surface. Such a tool member may be a rockable tool, which preferably comprises a convex face, such that the tool can be rocked about the convex face, with a plurality of substantially concentric raised arc formations on the convex face. The rockable tool is typically drawn along the opaque surface, advantageously in the general direction of the previously formed veined, grained or streaked appearance, so as to provide a heart grain effect on the opaque surface. This heart grain has been found to be especially aesthetically attractive. It is further preferred that as the rockable tool is drawn along the opaque surface, the convex face thereof is rocked in the direction of travel of the tool. The present invention is particularly advantageous in providing a decorated article, and a method of producing the same, which are largely free of organic solvents (except for small amounts of co-solvent). This aspect is environmentally beneficial, which is particularly advantageous when the resulting articles are found or used within building interiors. There is further provided by the present invention an article having a decorative coating, and obtained according to a method substantially as hereinbefore described. There is therefore provided by the present invention an article comprising: (a) a substrate having an opaque surface; (b) a decorative coating provided on said surface and comprising an intimate mixture comprising a particulate material and an aqueous film-forming polymer binder, said coating being lighter in colour than said surface and being discontinuously provided thereon so as to expose part of said surface. The nature of the substrate, opaque surface and decorative coating are substantially as hereinbefore described. The present invention is further illustrated in the accompanying drawings, in which: Figure 1 is a schematic view, by way of example, of the second stage of removal of the continuous layer in the method according to the invention; and Figures 2a, 2b and 2c respectively show end, side and plan elevations of the tool used in the method shown in Figure 1. Referring to Figure 1 , there is shown a hand 1 holding a rockable tool 2 which can be drawn in the direction of arrow A across a surface 3 having thereon a streaked or veined coating previously applied. Tool 2 has an elongate edge strip 4 and an elongate grip strip 5. Referring to Figures 2a, 2b and 2c, which show the tool in greater detail, the tool 2 is of generally pear-shaped cross-section (see Figure 2a), comprising an elongate grip strip 5 and, integral therewith, a bulbous edge strip 4 on which is a working face 6, which is concave and arcuate, such that the tool can be rocked as it is drawn over the surface 3. Working face 6 (as shown in Figures 2b and 2c) has a series of alternating arcuate raised ridges 7 and furrows 8, which are concentric and centred on an intermediate part 9 of the working face 6. (The working face and the ridges and furrows are not shown in detail in Figure 1.) The present invention will now be further illustrated by the following example which does not limit the scope of the invention in any way. A wood panel suitable for use as a building door was primed with white spirit based alkyd paint to receive a base coating of paint thereon. The paint for the base coating selected was light brown or beige (resembling the colour of light oak). The base paint was brushed onto a major face of the panel so as to provide a complete coating thereon and allowed to dry for two hours. An intimate mixture was prepared containing four parts plaster, four parts water, one part film-forming of an aqueous polyacrylate dispersion, one part of a cellulose based gel, and a small amount of an alcohol based co-solvent. The intimate mixture was applied onto the base paint coating so as to form a continuous layer thereon. A comb was drawn across the continuous layer, along the length of the panel, so as to penetrate to the paint coating and to discontinuously remove the layer and expose the underlying paint, and thereby provide an irregular veined appearance resembling that of natural grain, with the grains extending in a longitudinal direction of the panel. A rocking tool having a convex face with raised arc formations (as described above with reference to the drawings) was then drawn across the veined layer in the general direction of the previously provided veins; the convex face was drawn in the direction of travel of the rocking tool while at the same time slowly rocked, so as to produce a heart grain effect on the panel. The decorative grained layer was then allowed to dry, and a finishing varnish applied thereover. The result was an aesthetically pleasing, resembling the appearance of limed oak.

Claims: CLAIMS: 1. A method of providing a substrate with a decorative coating, which method comprises applying to an opaque surface of said substrate a substantially continuous layer comprising an intimate mixture comprising a particulate material and an aqueous polymer binder, said particulate material and said layer both being lighter in colour than said opaque surface, and discontinuously removing part of said layer so as to selectively expose part of said opaque surface. 2. A method according to claim 1 in which the particulate material comprises hydrated inorganic material. 3. A method according to claim 1 or 2, in which the intimate mixture in addition comprises reinforcing fibres and/or a drying retardant. 4. A method according to any of claims 1 to 3, in which the drying retardant comprises a gel. 5. A method according to any of claims 1 to 4, in which the binder comprises an aqueous suspension of acrylic polymer. 6. A method according to any of claims 1 to 5, in which the intimate mixture comprises 4 to 6 parts by weight of particulate material, 4 to 6 parts by weight of water, 0.5 to 3 parts by weight of aqueous polymer binder and 0.5 to 3 parts by weight of drying retardant. 7. A method according to any of claims 1 to 6, in which said opaque surface comprises an opaque coating. 8. A method according to claim 7, wherein said opaque coating is applied to said substrate as an aqueous formulation, prior to application of said substantially continuous layer. 9. A method according to any of claims 1 to 8, in which a translucent or transparent coating is applied to the decorative coating. 10. A method according to any of claims 1 to 9, in which the decorative coating is brown or beige in colour. 11. A method according to any of claims 1 to 10, in which the particulate material is white, cream, beige or brown in colour. 12. A method according to any of claims 1 to 11 , in which the decorative coating is applied and allowed to substantially dry prior to application of said intimate mixture. 13. A method according to any of claims 1 to 12, in which said intimate mixture is applied to said opaque surface as a substantially continuous layer to a thickness of 0.3 to 2mm. 14. A method according to any of claims 1 to 13, in which at least one tool member is employed for exposure of said opaque surface, said tool member being drawn along said opaque surface to provide a veined appearance. 15. A method according to claim 14, in which the tool member comprises an elongate, rockable convex face, having a plurality of substantially concentric arcuate ridges along the length thereof. 16. A method according to claim 15, in which the arcuate ridges are centred on an intermediate part of said length.

Inventors: PROSSER EDWARD, PROSSER, EDWARD
Applicants: PROSSER EDWARD, PROSSER, EDWARD
Application year: 1994
Main classification: B44F9
IPC codes: B05D3, B05D5, B44C3, B44D3, B44F9